Anaximenes of Miletus

Just as our soul, being air, constrains us, so breath and air envelops the whole kosmos.

Anaximenes of Miletus (c. 585 – c. 528 BC) was a Greek Pre-Socratic philosopher from the city of Miletus in Caria. He was reportedly a pupil of Anaximander, who himself followed the teachings of Thales in the Monist school of thought. Anaximenes is known for proposing air as the element from which all substances emanate (the material principle), for asserting that the universe is in constant motion, and for theorizing that the forms of matter change based on their rarity or density.

Or as Anaximenes of old believed, let us leave neither the cold nor the hot in the category of substance, but [hold them to be] common attributes of matter which come as the results of its changes. For he declares that the contracted state of matter and the condensed state is cold, whereas what is fine and 'loose' (calling it this way with this very word) is hot. As a result he said that it is not claimed unreasonably that a person releases both hot and cold from his mouth. For the breath becomes cold when compressed and condensed by the lips, and when the mouth is relaxed, the escaping air becomes warm because of rareness.

He says that the stars do not move under the earth as others have supposed, but around it, as a felt cap turns around our head. The sun is hidden not because it is under the earth but because it is covered by the higher parts of the earth and on account of the greater distance it comes to be from us. Because of their distance the stars do not give heat.

He [Anaximander] left Anaximenes as his disciple and successor, who attributed all the causes of things to infinite air, and did not deny that there were gods, or pass over them in silence; yet he believed not that air was made by them, but that they arose from air.